Constant output voltage rectifying system



SADAMICHI SOMEDA ET AL 3,405,345

CONSTANT OUTPUT VOLTAGE RECTIFYING SYSTEM Oct. 8, 1968 SSheets-Sheet 1Filed Nov. 14, 1966 FIG.|

W QMM M15440 ma Q human, ilk/M 1968 SADAMICHI SOMEDA ET AL 3,405,345

CONSTANT OUTPUT VOLTAGE RECTIFYING SYSTEM Filed Nov. 14, 1966 5Sheets-Sheet 2 (0) AC Supply Voltage (bwolfuqe of B (c)voltoge at A (d)Gofe Pulse (0) AC Supply Voltage (b) Voliuge of C ( c)Vol?age (B yAIEfi'Vl (d) voltage 7 (n-Vzl MA 7 6 lb\ (e) Gate Pulse J] Oct. 8, 1968SADAM|CH| SOMEDA ET AL 3,405,345

I CONSTANT OUTPUT VOLTAGE RECTIFY ING SYSTEM Filed Nov. 14, 1966 5Sheets-Sheet 5 8O 90 I00 H0 I20 AC Supply Voli'uge (\l) M'Mm 0 We wwlagizww United States Patent 3,405,345 CONSTANT OUTPUT VOLTAGE RECTIFYINGSYSTEM Sadamichi Someda, Hirakata-shi, Osaka-Eu, and Goro Harnano,Matsubara-shi, Osaka-fn, Japan, assignors to Matsushita ElectricIndustrial Co., Ltd., Osaka, Japan Filed Nov. 14, 1966, Ser. No. 594,085Claims priority, application Japan, Dec. 2, 1965, ill/75,442; Dec. 3,1965, 40/75,201 6 Claims. (Cl. 321-18) This invention relates to arectifying system for producing a substantially constant DC voltageregardless of any variation in the AC supply voltage and/or the loadcurrent, and more particularly it relates to a constant output voltagerectifying system having a rectifier with a controlling electrode, i.e.a gate, such as a silicon controlled rectifier.

In the following description, such a rectifier having a gate, such as asilicon controlled rectifier, will be referred to as an SCR forconvenience.

-Prior conventional constant output voltage rectifying systems having anSCR usually comprise a gate controlling circuit with a unijunctiontransistor. Such rectifying systems are generally complicated andexpensive.

It is an object of this invention to provide a constant output voltagerectifying system which has a simple construction.

It is another object of this invention to provide a voltage rectifyingsystem having an SCR and which produces a substantially constant -DCoutput voltage regardless of any variation in the AC supply voltageand/or the load current.

It is a further object of this invention to provide a constant DC outputvoltage rectifying system which employs a blocking oscillator whichcontrols an SCR.

These and other objects will be readily apparent to those skilled in theart from the following specification and accompanying drawings wherein:

FIG. 1 is a circuit diagram of a constant voltage rectifying system witha condenser input filter in accordance with the invention;

FIG. 2 is a circuit diagram of another constant voltage rectifyingsystem having a condenser input filter in accordance with the invention;

FIG. 3 is a graphical representation of the wave-form of the voltage atvarious parts of the circuit shown in FIG. 1;

FIG. 4 is a graphical representation of the waveform of the voltage atvarious parts of the circuit shown in FIG. 2;

FIG. 5 is a circuit diagram of still another rectifying system accordingto the invention; and

FIG. 6 is a graph showing the characteristic curve of the DC outputvoltage vs. AC supply voltage for the circuit of FIG. 5

Referring to FIG. 1, an AC power supply 1 is connected to the SCR 2which rectifies the power from power supply 1. The output side ofrectifier 2 is connected to a load 4 which has a condenser 3 connectedin parallel with the load and acts as an input filter to smooth theoutput of the rectifier which is fed to the load 4. On the other hand,the rectifier output voltage is divided into two parts by an outputvoltage dividing circuit having a resistor 6 and a non-linear resistanceelement 5 such as a Zener diode or a varistor. The non-linear resistanceelement has a characteristic voltagecurrent curve such that the currentincreases rapidly when the voltage ex- 3,405,345 Patented Oct. 8, 1968ceeds a predetermined voltage. The voltage from the resistor 6 issupplied to a transistor 7 as an emitter voltage. An integrating circuitis connected across the output side of SCR 2 and the output side of load4, and is composed of series connected resistors 8 and 9, and acondenser 10, and a diode 15 in parallel with the condenser 10. A pulsetransformer 11 is provided which has three windings, i.e., a primary, asecondary and a tertiary winding. The primary winding is connectedbetween point A between resistances 8 and 9 of the integrating circuitand the base of transistor. The secondary winding is connected to thecollector of the transistor, and the tertiary winding is connected inthe gate circuit of the SCR 2 with a resistor 12 in series therewith andwith a diode 16 connected in parallel therewith. The diode 16 isemployed to prevent a reverse voltage across the gate and cathode of theSCR 2. When a voltage at a point A between the resist ances 8 and 9 ofthe integrating circuit exceeds the emitter voltage, a blockingoscillator consisting of the pulse transformer 11 and the transistor 7operates and supplies to the gate of the SCR 2 a pulse through thetertiary winding of the pulse transformer 11 and through the resistor12. The pulse subsequently fires the SCR 2.

The voltages referred to hereinafter will be with reference to a voltageof the AC power supply 1 connected directly to the load 4 at zeropotential.

The AC voltage being supplied to the SCR 2 is divided by an inputvoltage dividing circuit having resistors 13 and 14 connected in series,and having the secondary winding of transformer 11 connected tointermediate point C, shown in FIG. 1. The transistor 7 is thus suppliedwith a collector voltage which is the divided AC voltage. The blockingoscillator does not operate during the first positive half cycle of theAC supply voltage E. During a negative half cycle of the AC supplyvoltage e, the transistor 7 operates in a reverse manner such that theemitter thereof acts as a collector and the collector acts as anemitter, and is supplied with a DC current from the input voltagedivider circuit. A condenser 17, coupled in parallel with resistor 6 ischarged and keeps the emitter voltage negative during the next positivehalf cycle of the AC supply voltage e. During the successive positivehal-f cycles, the blocking oscillator operates to produce a pulse in thegate circuit of the SCR which fires the SCR and consequently generatesan output voltage.

With regard to voltages at points A and B, the transistor 7 operates inthe reverse manner during a negative half cycle of the AC supply voltagee and as a result, as seen in FIG. 3, the voltage at the point A isapproximately equal to that at C. In addition, the voltage at B isblocked by the diode 15 and becomes --V which is defined as a voltagedrop :across the diode 15. When the voltage at C exceeds, during aninitial period of a positive half cycle, the voltgae V determined byresistors 8 and 9 and a load voltage, the operation of the transistor 7transfers from reverse to normal, that is, the emitter and the collectoract as an emitter and a collector, respectively. With the passage oftime, the voltage at B rises toward the load voltage along a curveaccording to a time factor determined by resistors 8 and 9 and thecondenser 10, and simultaneously the voltage at A rises along a curveaccording to the same time factor. When the voltage at C falls andbecomes the same as the voltage at A, i.e. V which is the voltage at Awhich has been rising during the period of the positive half cycle ofthe AC supply voltage, the operation of the transistor 7 is convertedfrom normal to reverse, and then the voltages at A and B start to fall.In

such a way, the voltage at A rises approximately linearly during thepositive half cycle of the AC supply voltage during a time intervalbetween a and b, as shown in FIG. 3.

The voltage across the resistor 6 is applied to the emitter of thetransistor 7 and is equal to a load voltage less the voltage drop Vcaused by the non-linear resistor 5, that is, E V for a load voltage ofE The voltage at A t='the time in reference to the time when thepolarity of be approximately represented as follows:

t=the time in reference to the time when the polarity of the AC supplyvoltage changes from negative to positive.

The voltage at A is equal to the base voltage of the transistor 7 exceptduring the time when the blocking oscillator is operating. At the timethe base voltage of the transistor 7 exceeds the emitter voltage, theblocking oscillator generates a pulse which fires the gate of the SCR 2and determine the conducting angle of the SCR 2. When the load voltageincreases to E because of a variation in the AC supply voltage and/ orthe load current, the emitter voltage of the transistor 7 be- "comes E Vand the voltage A is approximately represented as follows:

At the time the blocking oscillator operates. Now t t Therefore, theload voltage can be controlled so that it is lower in such a way thatthe position of the pulse which fires the SCR 2 moves back and then theconducting angle of the SCR 2 decreases. Consequently the load can beprovided with an approximately constant DC voltage depending upon thecircuit parameters of the non-linear resistor 5, resistor 6, 8 and 9,and the condenser by controlling the phase of the firing pulse for theSCR 2.

FIG. 2 is a circuit diagram of a constant voltage rectifying systemhaving a condenser input filter in accordance with the presentinvention. Voltage waveforms of the various parts of the circuit diagramof FIG. 2 are shown in FIG. 4. Referring to FIG. 2, reference character18 designates a non-linear resistor such as a varistor or Zener diodesin a back-to-back connection in place of the resistor 14 of FIG. 1. Thecircuit is otherwise the same as that of FIG. 1 and the referencecharacters in FIG. 2, correspond to those of FIG. 1. A substantiallyconstant voltage is supplied to the collector of transistor 7 duringnormal operation by causing the voltage at point C to have a nearlysquare waveform as shown in FIG. 4b. As a result, the amplitude of thegate firing pulse is approximately constant and the operation of therectifying system can be stabilized.

A specific embodiment of this invention is set forth in the followingexample. However, this example should not be construed as limitative.

In connection with FIG. 5, which shows a circuit diagram having anadditional resistor 19 and a condenser input filter 3, and has thedirection of the rectifiers and diodes reversed, the elements have thefollowing specified values:

SCR 2 2F265 Condenser 3 rnicrofarads 2000 Load 4 ..ohms or infinite-..26 Varistor 5 volts at 10 ma 7 '15 Resistor 6 ohms 330 Transistor 72SB176 Resistor 8 ohms 68K Resistor 9 do 18K Condenser 10 -microfarad 1Pulse transformer 125T-125T-250T Resistor 12 o-hms Resistor 13 do 6KDiode 15 0A95 Diode 16 0A95 Condenser 17 microfarads 10 Varistor 18"volts at 10 ma 22 Resistor 19 "ohms" 19 The characteristic curves ofthe circuit diagram of FIG. 5 are shown in FIG. 6 at a load resistanceof 26 ohms and at no load. It will be readily understood from FIG. 6that the rectifying system described can generate a DC output voltage of27.2 v.i3.86% where the AC supply voltage is 100 v.:20% in accordancewith the present invention.

What is claimed is:

1. A constant output voltage rectifying system, comprising a rectifierhaving an anode, a cathode and a gate means, said rectifier having aninput side adapted to be coupled to a source of AC voltage; an inputfilter means coupled in series with the output side of said rectifierand adapted to be coupled in parallel with a load; an output voltagedividing circuit connected to the output side of said rectifier andadapted to be in parallel with a load and having a resistor, a condenserconnected in parallel with said resistor, and a non-linear resistanceelement connected in series with said condenser, said non-linearresistance element having a voltage-current characteristic such that thecurrent flowing therein increases rapidly when the voltage thereofexceeds a predetermined voltage; an input voltage dividing circuitcoupled in parallel with said source of AC voltage and having tworesistance means connected in series; an integrating circuit having afurther condenser, a diode connected in parallel to said furthercondenser and two resistors connected in series with said diode, saidintegrating circuit being connected to the output side of said rectifierwith said resistances between said condenser and said rectifier andadapted to be in parallel with a load, and a blocking oscillator havinga transistor with an emitter, a collector and a base, and a pulsetransformer having a primary, secondary and tertiary winding, one end ofthe primary win-ding being connected to said input voltage dividingcircuit between said resistance means and the other end connected tosaid collector of the transistor, one end of the secondary winding beingconnected to said integrating circuit between said resistances and theother end being connected to the base of said transistor, and thetertiary Winding of said transformer being connected across said gatemeans and said cathode of rectifier, said emitter of transistor beingconnected to said output voltage dividing circuit between said resistorand said non-linear resistance element there- 2. A rectifying system asclaimed in claim 1 in which said non-linear resistance element in saidoutput voltage dividing circuit is a Zener diode.

3. A rectifying system as claimed in claim 1, in which said non-linearresistance element in said output voltage dividing circuit is avaristor.

4. A rectifying system as claimed in claim 1 in which one of said tworesistance means in said input voltage dividing circuit is a non-linearresistance.

5. A rectifying system as claimed in claim 1 in which one of said tworesistance means in said input voltage dividing circuit is a varistor.

6. A rectifying system as claimed in claim 1 in which one of said tworesistance means in said input voltage dividing circuit is two Zenerdiodes connected in backto-back relationship.

References Cited UNITED STATES PATENTS Clarke et a1 32322 XR Deelman32l-18 Clarke et a1. 323-22 Biet 32322 XR

1. A CONSTANT OUTPUT VOLTAGE RECTIFYING SYSTEM, COMPRISING A RECTIFIERHAVING AN ANODE, A CATHODE AND A GATE MEANS, SAID RECTIFIER HAVING ANINPUT SIDE ADAPTED TO BE COUPLED TO A SOURCE OF AC VOLTAGE; AN INPUTFILTER MEANS COUPLED IN SERIES WITH THE OUPUT SIDE OF SAID RECTIFIER ANDADAPTED TO BE COUPLED IN PARALLEL WITH A LOAD; AN OUTPUT VOLTAGEDIVIDING CIRCUIT CONNECTED TO THE OUTPUT SIDE OF SAID RECTIFIER ANDADAPTED TO BE IN PARALLEL WITH A LOAD AND HAVING A RESISTOR, A CONDENSERCONNECTED IN PARALLEL WITH SAID RESISTOR, AND A NON-LINEAR RESITANCEELEMENT CONNECTED IN SERIES WITH SAID CONDENSER, SAID NON-LINEARRESISTANCE ELEMENT HAVING A VOLTAGE-CURRENT CHARACTERISTIC SUCH THAT THECURRENT FLOWING THEREIN INCREASES RAPIDLY WHEN THE VOLTAGE THEREOFEXCEEDS A PREDETERMINED VOLTAGE; AN INPUT VOLTAGE DIVIDING CIRCUITCOUPLED IN PARALLEL WITH SAID SOURCE OF AC VOLTAGE AND HAVING TWORESISTANCE MEANS CONNECTED IN SERIES; AN INTEGRATING CIRCUIT HAVING AFURTHER CONDENSER, A DIODE CONNECTED IN PARALLEL TO SAID FURTHERCONDENSER AND TWO RESISTORS CONNECTED IN SERIES WITH SAID DIODE, SAIDRECTIFIER WITH SAID RESISTANCES BETHE OUTPUT SIDE OF SAID RECTIFIER WITHSAID RESISTANCES BETWEEN SAID CONDENSER AND SAID RECTIFIER AND ADAPTEDTO BE IN PARALLEL WITH A LOAD, AND A BLOCK OSCILLATOR HAVING ATRANSISTOR WITH AN EMITTER, A COLLECTOR AND A BASE, AND A PULSETRANSFORMER HAVING A PRIMARY, SECONDARY AND TERTIARY WINDING, ONE END OFTHE PRIMARY WINDING BEING CONNECTED TO SAID INPUT VOLTAGE DIVIDINGCIRCUIT BETWEEN SAID RESISTANCE MEANS AND THE OTHER END CONNECTED TOSAID COLLECTOR OF THE TRANSISTOR, ONE END OF THE SECONDARY WINDING BEINGCONNECTED TO SAID INTEGRATING CIRCUIT BETWEEN SAID RESISTANCE AND THEOTHER END BEING CONNECTED TO THE BASE OF SAID TRANSISTOR, AND THETERTIARY WINDING OF SAID TRANSFORMER BEING CONNECTED ACROSS SAID GATEMEANS AND SAID CATHODE OF RECTIFIER, SAID EMITTER OF TRANSISTOR BEINGCONNECTED TO SAID OUTPUT VOLTAGE DIVIDING CIRCUIT BETWEEN SAID RESISTORAND SAID NON-LINEAR RESISTANCE ELEMENT THEREIN.